it could be bad or stripped gears. Ultimately i have never had a problem with the servos i have used (Savox, Xpert, JX) so unfortunately cant help much more without physically seeing it. someone else may be able to help but I feel that it could be broken or stripped gears.
Best thing you can do is send back to hobbyking and get a new one or go all out and get a name brand such as Savox.